Conventionally, a thermistor element that can measure extremely high temperatures of approximately 1000° C. is required in a sensor for measuring a catalyst temperature, an exhaust system temperature, or the like that is disposed in the periphery of an automobile engine. A thermistor element generally includes a metal-oxide sintered body (for example, a perovskite Y (Cr,Mn)O3) and a Pt wire. Resistance to a heat cycle from room temperature to 1000° C. is imparted by insertion of two Pt wires into the a metal-oxide sintered body, and strongly fixing the Pt wires by sintering using a metal oxide.
Consequently, the Pt wire must be inserted prior to sintering of the metal oxide, and the metal oxide and the Pt wire must be fired at the same time. Since heat resistance properties to 1000° C. are required, the metal oxide should preferably have a sintering temperature of at least 1400° C., and for that reason, Pt wire that is stable at a temperature of at least 1400° C. is used in the electrode.
Conventionally, as disclosed in Patent Literature 1, a method of manufacturing a high-temperature thermistor that embeds Pt wire includes a powder-press method that applies a pressing operation to the metal wire at the same time as a granulated ceramic powder.